1. Field of the Invention
The present invention relates to the field of pressure-measuring technology. It relates to a pressure-measuring device for measuring pressure fluctuations in a space which is filled with hot gases at a first temperature and is delimited by at least one wall from an outer space which is at a lower second temperature, in particular for measuring pressure fluctuations in the combustion chamber of a gas turbine, in which pressure-measuring device a measuring tube largely free of end reflections with regard to the pressure fluctuations is passed from the space through the at least one wall into the outer space, and in which, in the outer space behind the at least one wall, a pressure sensor for sensing the pressure fluctuations is connected to the measuring tube.
Such a pressure-measuring device is known in principle from the prior art.
2. Discussion of Background
It is known to measure pressure fluctuations in a combustion chamber, in which hot gases are under varying pressure conditions, using a comparatively simple device and with considerable accuracy. The device consists of a long thin tube which has a length of about 20 m and is connected with one end to the combustion chamber at the location where the pressure or the pressure fluctuations are to be measured. The actual pressure sensor is connected laterally to the thin measuring tube outside the hot combustion chamber in the markedly colder ambient. It is thereby possible to use a more cost-effective pressure sensor, which does not have to withstand the high temperatures in the combustion chamber. At the same time, simplified access to the pressure sensor arranged on the outside is obtained, as a result of which maintenance and repair are simplified and their costs are reduced.
The essential idea behind the pressure-measuring device described is to design the measuring tube, which forms an acoustic line for the pressure oscillations to be measured, in such a way that virtually no pressure waves are reflected in the tube within a large frequency range and thus distort the measurements taken with the pressure sensor. The long thin tube serves to exponentially dampen the pressure waves running into the tube from the measuring location, so that reflections from the tube back to the pressure sensor are largely avoided.
Despite the exponential damping of the measuring tube, however, problems with wave reflections may occur. If there are comparatively abrupt temperature changes over the length of the measuring tube, as inevitably arise when the tube is passed to the outside from a combustion chamber through an intermediate space having multiple shielding, reflections of the pressure waves running in the tube may be caused at these jumps in temperature and these reflections arrive back at the pressure sensor and distort the measurement there. In the process, the distortion of the measurements increases with increasing frequency of the pressure oscillations.